This invention relates to a guard rail detecting device in which an optical distance detecting device using an image sensor operates to measure the distance between a motor vehicle and a guard rail located ahead of it, thereby to predict the curvature of the guard rail.
An optical distance detecting device using an image sensor has been disclosed in the art, for instance, by Japanese Patent Examined Published Application Nos. Sho-63-38085/(1988) and Sho-63-46363/(1988). The device, as shown in FIG. 6, has two right and left optical systems having two lenses 1 and 2 which are spaced by a base length L from each other. Image sensors 3 and 4 are disposed at the focal length f of the two lenses 1 and 2, respectively. The output image signals of the image sensors 3 and 4 are applied to a signal processing unit 30, where they are shifted so as to be electrically superposed on each other. When the two image signals are superposed to the best possible extent, the amount of shift (l) is read to calculate the distance (R) between the position of the lenses and an object 31 from the following expression according to the trigonometrical measurement principle: EQU R=(f.times.L)/l
On the other hand, a method of detecting the radius of curvature of a curved road along which a motor vehicle is traveling has been disclosed, for instance, by Japanese Unexamined Published Application No. Hei-1-285815/(1990). In the conventional method, a gyroscope or a geomagnetic sensor is employed to detect the radius of curvature of a curved road along which a motor vehicle is traveling.
In the case of the above-described conventional method, in order to detect the radius of curvature of a curved road, it is essential that the motor vehicle is already traveling along the curved road. Furthermore, the radius of curvature of a road cannot be detected before the motor vehicle reaches the curve int he road. Hence, even if there is a sharp turn ahead of the motor vehicle, it is impossible to warn the driver.